Improve error message when no suitable file is found

[severo]

See https://huggingface.co/datasets/wefussell/amasum_neg/discussions/1#654d1c3671a30c4bcaf9fb77

It contains the following tree:

The files have no extensions, so datasets cannot get the list of configs. But the error message mentions a dataset script. Now that we "deprecated" the datasets scripts in the dataset viewer, it's confusing for the users. The error message is:

Error code:   ConfigNamesError
Exception:    FileNotFoundError
Message:      Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg. 
Traceback:    Traceback (most recent call last):
                File "/src/services/worker/src/worker/job_runners/dataset/config_names.py", line 65, in compute_config_names_response
                  for config in sorted(get_dataset_config_names(path=dataset, token=hf_token))
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 351, in get_dataset_config_names
                  dataset_module = dataset_module_factory(
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/load.py", line 1508, in dataset_module_factory
                  raise FileNotFoundError(
              FileNotFoundError: Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg.

We should instead return an error message with a specific error code (different from "ConfigNamesError") so that the Hub can show a specific message, pointing to the new docs.

[severo]

I think it's an issue in the datasets library because it gives the same error for:

• https://huggingface.co/datasets/severo/a_dataset_that_does_not_exist: a dataset that does not exist
• https://huggingface.co/datasets/severo/test_files_without_extension: a dataset with files without a known extension

>>> import datasets
>>> datasets.get_dataset_config_names('severo/a_dataset_that_does_not_exist')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 351, in get_dataset_config_names
    dataset_module = dataset_module_factory(
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/load.py", line 1508, in dataset_module_factory
    raise FileNotFoundError(
FileNotFoundError: Couldn't find a dataset script at /home/slesage/hf/datasets-server/services/worker/severo/a_dataset_that_does_not_exist/a_dataset_that_does_not_exist.py or any data file in the same directory. Couldn't find 'severo/a_dataset_that_does_not_exist' on the Hugging Face Hub either: FileNotFoundError: Dataset 'severo/a_dataset_that_does_not_exist' doesn't exist on the Hub. If the repo is private or gated, make sure to log in with `huggingface-cli login`.
>>> datasets.get_dataset_config_names('severo/test_files_without_extension')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 351, in get_dataset_config_names
    dataset_module = dataset_module_factory(
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/load.py", line 1508, in dataset_module_factory
    raise FileNotFoundError(
FileNotFoundError: Couldn't find a dataset script at /home/slesage/hf/datasets-server/services/worker/severo/test_files_without_extension/test_files_without_extension.py or any data file in the same directory. Couldn't find 'severo/test_files_without_extension' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in severo/test_files_without_extension.

To differentiate, we have to parse the error message (only the end is different). We should have a different exception for these two errors.

[severo]

I created huggingface/datasets#6397.

[severo]

Note: huggingface/datasets#6397 has been fixed in datasets, with huggingface/datasets#6431.

Waiting for a release

[severo]

Done.